For example, a metal grating for X-ray receiving X-rays is utilized in various apparatuses as an element including a number of parallel periodic structures, and in recent years, application to an X-ray imaging apparatus has been attempted. In this X-ray imaging apparatus, in recent years, X-ray phase imaging has been attracting attention in view of reduction in an exposure amount, for example, a Talbot interferometer or a Talbot-Lau interferometer has been applied. In this X-ray imaging apparatus including the Talbot-Lau interferometer, three metal gratings for X-ray of a 0-th grating, a first grating, and a second grating are used. This 0-th grating is a normal grating utilized to change a single X-ray source to a multi-light source, and divides an X-ray radiated from the single X-ray source into a plurality of X-rays (a plurality of X-ray beams) to radiate the same. These first and second gratings are diffraction grating disposed apart from each other by a Talbot distance to configure a Talbot-Lau interferometer (or Talbot interferometer). In this diffraction grating, when classified in a diffraction method, generally, there are a transmission type diffraction grating and a reflection type diffraction grating, and further, in the transmission type diffraction grating, an amplitude type diffraction grating (an absorption type diffraction grating) in which portions absorbing light are periodically arrayed on a substrate transmitting the light, and a phase type diffraction grating in which portions changing a phase of the light are periodically arrayed on a substrate transmitting the light.
The above-described X-ray phase imaging requires the absorption type diffraction grating, in which contrast between the portions transmitting X-rays and the portions not transmitting X-rays is distinct, and the phase type diffraction grating, in which a phase difference is distinct. Therefore, a grating of a high aspect ratio structure, which has a very high aspect ratio, for example, 3 or more is required. Therefore, a production method of applying a processing technique of a semiconductor has been proposed, and for example, in Japanese Unexamined Patent Application Publication No. 2017-32476, a method for manufacturing a high aspect ratio structure has been disclosed. The method for manufacturing the high aspect ratio structure disclosed in Japanese Unexamined Patent Application Publication No. 2017-32476 includes a hole formation step of forming a plurality of holes in at least one main surface of a substrate, a resist formation step of forming first regions where a resist layer is provided, and second regions where the resist layer is not provided in the main surface where the plurality of holes are formed after the hole formation step, and a recess formation step of forming recesses in the substrate corresponding to the second regions by immersing the substrate in an etching liquid.
Moreover, the above-described high aspect ratio structure can also be found in an ultrasonic probe.
In the method for manufacturing the high aspect ratio structure disclosed in Japanese Unexamined Patent Application Publication No. 2017-32476, a wet etching method is used. In this wet etching method, in a drying step of drying a workpiece after subjecting the workpiece to the wet etching, a phenomenon of sticking that the structure sticks attributed to a surface tension of the etching liquid may occur. Particularly, since the high aspect ratio structure has projections having a high aspect ratio, the sticking more easily occurs in the projections.